1. Field of the Invention
The present invention relates to a mobile radio communication system estimating the position of moving bodies, particularly, the positional relationship between an own moving terminal and another moving terminal. The present invention is useful for moving bodies running in an environment in which blind spots are likely to be caused due to, for example, buildings. The present invention is applicable to, for example, a safety assistance system to be provided to ensure traffic safety at, for example, a blind intersection.
2. Description of the Related Art
For example, a Japanese Unexamined Patent Application Publication No. 2006-107521 discloses a moving terminal communication apparatus. Such a communication apparatus transmits and receives the position and speed of a respective vehicle to and from other vehicles with communication devices performing dedicated short range communication (DSRC) and reception devices receiving signals from a global positioning systems (GPS). And the apparatus alerts the driver to the presence of another vehicle within a close range. In addition, a traffic safety system assisting safety driving is expected to be developed in recent years. The traffic safety system uses a vehicle-to-vehicle communication system including the moving terminal communication apparatuses mounted in vehicles to detect the position and speed of another approaching vehicle in order to estimate the risk of, for example, a head-on collision at an intersection and to indicate the estimated risk to the driver in advance.
However, in such DSRC technologies in related art, when another vehicle is positioned outside the visual range (in a blind spot) of the own vehicle because of the presence of a building or the like, the establishment of the DSRC between the vehicles, that is, the transfer of the position and speed of the own vehicle between the vehicles is likely to fail. Because the electromagnetic waves are drastically attenuated due to the diffraction of electromagnetic waves. For the same reason, it is not easy to ensure a sufficient communication distance between the own vehicle and another hidden vehicle. Accordingly, there is a problem in that the safety of the vehicles cannot be necessarily ensured sufficiently in the related art.